The present invention relates to a refrigerating apparatus and more particularly to a parallel operation compressor type refrigerating apparatus comprising compressors operable in parallel with each other, wherein the lubricant levels in the compressors are always maintained appropriately equal regardless of whether the compressors are operated in parallel with each other or any one of them is operated singularly.
Hitherto, in a parallel compression type refrigerating apparatus comprising two compressors, a pressure and lubricant equalizing pipe has been provided between the two compressors and adapted to always keep the compressors in communication with each other during the operation of the compressors, whether that operation be parallel or singular. As a result, in a semi-hermetically sealed refrigerating machine in which a suction element chamber and a compressing element chamber are separated by a partition, since during a singular operation a pressure is applied to the compressing element chamber of the compressor which is in operation through a suction pipe, a motor chamber, the compressing element chamber, and the pressure and lubricant equalizing pipe of the compressor which is not in operation, a lubricant equalizing nonreturn valve in the compressor which is in operation is closed so that the lubricant returned into the suction chamber cannot be returned into the compressing element chamber, making it difficult to maintain the lubricant level in a compressing element chamber at a normal level, so that seizure of the shifting portions of the compressor due to a shortage of the lubricant thereto, a decrease in refrigeration capacity due to excessive lubricant content in the compressor which is in operation, damage of valve portions due to the compression of the lubricant, etc. may occur.
There is a solution to prevent excessive lubricant during the partial operation of the compressors. It is to mount a lubricant separator at the discharge side of the compressor to separate the lubricant oil contained in the discharged gas, returning the separated lubricant oil to the compressor. However, this known procedure has various defects, such as that the lubricant at a high temperature raises the lubricant temperature in the crankcase when the former returns there, and that when the compressor is started again after a standstill of a long time condensed liquid refrigerant in the lubricant separator at a low temperature is returned to the compressor to foam the lubricant, resulting in deterioration of the lubrication, etc. Moreover, due to a slight difference in capacity between the two compressors and a difference in the pipe friction of the suction pipes, a differential pressure is generated between the compressing element chambers of the two compressors so that a tendency for the lubricant levels not to be equal develops. There is also another defect, i.e. since the lubricant level is hard to observe through a sight glass, maintenance is difficult.